1. Field of the Invention
Rotating thermal machines for very high duties. The critical component is the blading which has to ensure the greatest possible life under strongly fluctuating mechanical and thermal conditions.
The invention concerns the further development of highly loaded blading for rotating thermal machines, in particular for gas turbines, while permitting optimum selection of material for the various parts. Oxide-dispersion-hardened alloys should preferably also be given consideration for the airfoil.
In particular, it concerns a method for manufacturing rotating thermal machine blading consisting of an airfoil, a root and a shroud plate or shroud by fastening a shroud plate or a shroud to the tip of the airfoil.
It also concerns rotating thermal machine blading consisting of an airfoil, a root and a shroud plate or shroud, either of the latter two being fastened to the tip of the airfoil.
2. Discussion of Background
Shroud plates and shrouds on nozzle guide vane and rotor blade rows of rotating thermal machines (steam and gas turbines) are used to improve the flow conditions (aerodynamics) and the thermal efficiency (thermodynamics) of the machine. In addition, they are intended to improve the vibration behavior, in particular of rotors, by modifying the natural frequencies and increasing the damping. In mechanical engineering practice, numerous ways of fastening shroud plates and shrouds to the tip of the blading are known. In steam turbines, riveted shrouds are often found on the end surface of the tip of the blades. Shroud plates can also be manufactured from the solid by machining or by casting. On this subject, the following literature can, inter alia, be cited.
Walter Traupel, Thermische Turbomaschinen, Vol. 2 Regelverhalten, Festigkeit und dynamische Probleme, Springer Verlag 1960 PA0 H. Petermann, Konstruktion und Bauelemente von Stromungsmaschinen, Springer Verlag 1960 PA0 Fritz Dietzel, Dampfturbinen, Georg Lieberman Verlag 1950 PA0 Fritz Dietzel, Dampfturbinen, Berechnung, Konstruktion, Carl Hauser Verlag 1980 PA0 C. Zitemann, Die Dampfturbinen, Springer Verlag 1955.
In recent times, oxide-dispersion-hardened nickel-based superalloys have been proposed as blading materials for highly loaded gas turbines because they permit operating temperatures which are higher than those of conventional cast and forged superalloys. In order to achieve the best strength values (high creep strength) at high temperatures, components made from these alloys are employed with coarse longitudinally extended crystalites directed along the blade axis. During the manufacturing process, the workpiece (semi-finished product or finished part) must generally be subjected to a zone heat treatment process. For various reasons (thermodynamics, crystallisation laws), there are limits to the cross-sectional dimensions of such blade materials in the coarse-grained condition. This also imposes limits on the blade dimensions. Because the area of a shroud plate is generally a multiple of the cross-sectional area of the corresponding airfoil, there are dimensions beyond which it becomes impossible to manufacture the blading and the shroud plate monolithically from one piece. If oxide-dispersion-hardened superalloys are to be successfully and generally employed, there is therefore a requirement for the component to be divided into the blade airfoil, on the one hand, and the shroud plate, on the other.
Numerous frictional connections between structural elements using wedges, pins, wires, etc. are known in general mechanical engineering. Such elements are often used for locking purposes only. There is an increasing tendency to use oxide-dispersion-hardened superalloys as blading materials in the gas turbine industry. There is therefore a need for further development of operationally satisfactory constructions in this field.